The present invention relates to biological indicators of sterilization and disinfection.
Primarily in the health care industry, but also in many other industrial applications, it is nearly always necessary to monitor the effectiveness of the processes used to sterilize equipment such as medical and non-medical devices, instruments and other articles and materials. In these settings, sterilization is generally defined as the process of completely destroying viable microorganisms including structures such as viruses and spores. Standard practice in these health care facilities is to include a sterility indicator in the batch of articles to be sterilized. The use of sterility indicators allows a direct and sensitive approach to assay the lethality of the sterilization process.
A standard type of biological sterility indicator includes a presumably known quantity of test microbial spores. This indicator is placed into the sterilization chamber and exposed to the sterilization process along with the objects to be sterilized. The test microorganisms, for example Bacillus stearothermophilus or B. subtilis spores, are then contacted with a growth medium and incubated for a specified period of time under conditions which favor proliferation and examined for possible growth, as determined by the presence or absence of certain metabolic products, of any surviving microorganisms. Positive growth indicates that the sterilization process was insufficient to destroy all of the microorganisms. While a wide variety of apparatuses for containing the spores have been developed, there are few variations in the general sterility detection process.
Prior biological indicators disclosed in existing patents contain a preparation of viable spores made from a culture derived from a specific bacterial strain and characterized for predictable resistance to sterilization. Spores of bacteria are often the test organism in conventional biological indicators because they are much more resistant to the sterilization process than most other organisms. Many of the prior art biological indicators are self-contained, meaning that they possess the spores and the incubation media in a single container but typically in separate compartments. Following sterilization, the container is processed so that the spores come into contact with the growth media. The entire container is then incubated for a specific time and the results determined and recorded.
Alternatively, some biological indicators are comprised of spores on a carrier in a package. After being exposed to the sterilization process, the carrier with the spores is transferred from the package to sterile media and incubated.
A major drawback of all these sterility indicators is the time delay in obtaining results of the sterility test. These sterility indicators normally require that the microorganisms be cultured for at least two and often up to seven days to assure adequate detection of any surviving microorganisms. During this time, the items which went through the sterilization process should not be used until the results of the spore viability test have been determined. A viable spore result indicates that proper sterilization conditions were not met.
Many health care facilities have limited resources and must reuse their “sterilized” instruments within 24-48 hours and often immediately. In such settings, the three to seven day holding period for sterility verification is impractical, costly and inefficient.
There are even further time delays and costs necessitated by these traditional commercial biological indicators because technicians must be trained and clean room facilities must be made available in order to determine the viability of the biological indicators using standard microbiological techniques.
Further, most of the conventional growth tests are performed in test facilities outside the medical or dental offices where the sterile instruments are used and prepared, thereby further compounding the costs and delay in obtaining the test results.
The use of an enzyme and its subsequent activity as an indicator in an attempt to overcome the time delay in detecting sterility has also been described previously. While obviating the need for complex sample handling and decreasing the processing time required by biological indicators, the use of enzyme, or multiple enzymes, also have disadvantages. For example, the specialized equipment is often necessary to detect the product made by a single enzyme. Additionally, the use of a single or multiple enzymes does not effectively recreate the response of a complex, living organism to a sterilization process. Thus, the response of an enzyme or enzymes to a sterilization treatment may not properly reflect efficacy of sterilization with respect to biological organisms. That is, although thermostable enzymes may be useful in determining the effectiveness of a sterilization process, they do not provide the same degree of sterilization assurance as do live bacterial spores as biological indicators. Because the activity of a thermostable enzyme can only be correlated with spore death, the degree of inactivation of such an enzyme may not accurately measure the effect of the sterilization process on a living organism in all instances. Low numbers of surviving organisms may not produce sufficient enzyme to break down the indicator substrate so that a color change or colorimetric reading is registered, thereby giving a false negative. Furthermore, the enzyme assay does not function for cold sterilization treatments.
Therefore, there is a need for a biological indicator and methods for the use thereof to accurately detect the efficacy of a sterilization treatment which indicator does not require complex processing and which yields rapid results, i.e., results are obtained in a matter of hours instead of days. The present invention meets this need.